Perforated trays with downcomers are one of the most commonly used internals in industrial columns for contacting a gas and a liquid. In such columns, liquid flows across the trays and down through the downcomers, from tray to tray, while gas permeates upwardly through the trays foaming liquid thereon.
Many perforated trays are a simple sieve tray, i.e., a sheet with an array of circular perforations or holes. Some perforated trays have valves or fixed deflection caps covering the perforations to increase the contact between the liquid and the gas and thus enhance the efficiency and the gas/liquid handling capacity of the column containing the trays.
Columns containing perforated trays, may be used in, for example, processes where distillation, absorption and stripping operations are involved and wherein solids are present in particulate form, see, for example, xe2x80x9cSubdue Solids in Towerxe2x80x9d A. W. Stoley et al, xe2x80x9cDistillation and Other Industrial Separationxe2x80x9d, page 95 to 104, dated January 1995, published in Chemical Engineering Progress.
Stoley et al, L/H column, page 97, under the heading xe2x80x9cBasic Approachesxe2x80x9d states that when solids are unavoidable, the best approach is to keep them moving, and that designing the equipment to keep them moving is critical. The more active the liquid, the lower the probability of plugging. Further, Stoley et al, page 98, L/H column, under xe2x80x9cTraysxe2x80x9d states that bubble cap trays have been commonly used in solids containing systems and, having large open spaces, prevent blockage by solids"" sedimentation. The disadvantages with bubble-cap trays is that they are expensive, have low capacity, and are not suitable in high-solids-loading services with particles that stick to the tray.
U.S. Pat. No. 3,463,464, dated Aug. 26, 1969, and U.S. Pat. No. 5,360,583, dated Nov. 1, 1994, improved the efficiency and capacity by providing trapezoidal openings in the plane of the tray deck and a stationary deflector overlying each opening and aligned therewith. The deflector, and the adjacent deck surface, defines lateral outlet slots which are oriented to direct vapor passing up through that aperture in generally transverse directions to the flow of liquid across the deck.
While these trapezoidal openings and stationary deflectors are an improvement, there is still a problem in that gas tends to flow back on the stationary deflector causing build-up of, and fouling by, solids at a downstream ends of the stationary deflectors, thus reducing the efficiency and capacity of the column.
There is a need for a gas/liquid contacting, perforated tray assembly, wherein back flow on a stationary deflector or cover strip is reduced thereby reducing build-up and fouling by solids at the downstream ends of the stationary deflectors or cover strips.
According to the present invention there is provided a gas/liquid contacting, perforated tray assembly, comprising,
a) a perforated sheet having an array of elongated openings, whereby, in operation, liquid flowing over the sheet, and along the openings, will be mixed with gas flowing upwardly through the openings, and, for each opening,
b) an elongated cover strip, arching upwardly over and spanning the length of that opening, and having a slot extending from one end thereof into an upper portion thereof, and
c) a liquid conveying strip in the slot and having a first portion extending along a bottom portion of the slot, from the said one end, and a second, portion sloping upwardly to the top of the cover to provide,
i) a liquid path along the slot, and
ii) side outlets for directing gas from the opening into each side of the liquid path.
Preferably each slot extends from an upstream end of the cover strip.
In some embodiments of the present invention, each elongated opening, and cover strip therefor, are tapered inwardly in the downstream direction.
In other embodiments of the present invention the liquid conveying stip is a first liquid conveying strip, and each cover strip has a second slot extending from an opposite end to the said one end into an upper portion thereof, and, for each second slot there is provided a further liquid conveying strip in that slot, each further liquid conveying strip having a first portion extending progressively downwardly from the cover strip to a lower portion of that slot, and a second portion extending along a bottom portion of that slot, to provide,
i) a second liquid path along the slot, and
ii) side outlets for directing gas from the opening into each side of the second liquids path.
Each elongated-opening, and cover strip therefor, may be tapered inwardly across the width in the liquid downstream direction.
The cover strips and the liquid conveying strips may be integral with the perforated sheet.
In other embodiments of the present invention, the cover strips, and the conveying strips are integral with the perforated sheet.
In this specification, upstream and downstream means upstream and downstream of liquid flow across a perforated tray.